Coughing, or the sudden, forcible expulsion of air at high velocity, is invariably accompanied by sounds having selected frequency characteristics and differing intensities. Patients with persistent nocturnal coughs frequently complain of sleep disruption caused by the cough reflex, as do those capable of hearing the oft-unpleasant sounds associated with the coughs, including parents of acutely or chronically ill children. To both the patient and those in close proximity, therefore, suppression of the patient's cough reflex desirable. This desirability has led to experimentation with a wide variety of substances as antitussive agents, with the experimentation itself causing a parallel effort to develop methods for accurately and uniformly determining the effectiveness of these medications.
Early attempts at artificially inducing coughing with chemical irritants or using subjective responses in ascertaining effectiveness have been largely unproductive and widely criticized. Artificially inducing coughs leads to increasingly inaccurate measurements as patients develop tolerances to the irritants, while varying the frequency and intensity of the coughs as a function of the concentration of the irritant and the interval between exposures. Although subjective responses may provide valuable evidence of patients, beliefs as to effectiveness, they lack readily quantifiable information useful for comparing the wide range of competing antitussives. In addition, controlled studies have shown the potentially grossly misleading nature of purely subjective responses.
More recent attempts at objectively determining the usefulness of antitussives have included tape recorders as means for capturing sound information concerning coughs emitted by patients. As discussed in Sevelius and Colmore, "Objective Assessment of Antitussive Agents in Patients with Chronic Cough," The Journal of New Drugs 216-23 (July-August 1966), sound information related to coughing can be transmitted to a recorder using a throat microphone taped to a patient. Evaluation of the antitussive includes counting the coughs emitted by each patient, a process conducted by manually reviewing the tape recording for each patient. According to Sevelius and Colmore, although intrusive, the throat microphone and attached wiring does not prevent patients from watching television or moving relatively freely throughout a room. Such an intrusive system is, however, likely to disrupt normal sleeping patterns, decreasing both the comfort levels and movement abilities of patients wearing the throat microphones.
Other devices presently used for monitoring the onset of coughs often include a belt worn about the abdomen of the patient and sensors maintained in contact with the body. Typical of these devices are those described in U.S. Pat. Nos. 4,413,620 and 4,240,444 to Tucker and Virgulto, et al., respectively. The patent to Tucker, for example, discloses an abdominal restraint system having a belt designed to inflate in response to signals associated with the onset of coughs. Pressure sensors inserted into the patient using catheters or mounted within the belt are used to detect internal body motion associated with coughing. The apparatus disclosed in Virgulto, et al. similarly includes a belt attached to the patient's body and uses a protruding, displaceable disc to contact a sealed bulb and change its pressure relative to the atmosphere.
Although both the Tucker and Virgulto, et al. devices respond to the onset of coughing, neither apparatus is designed to evaluate the effectiveness of cough-resisting medications by counting the number of coughs emitted. As with the system of Sevelius and Colmore, the intrusiveness of these devices additionally limits their use as evaluation tools in nocturnal environments. Discomfort felt by patients while wearing the devices is likely to inhibit normal sleeping patterns, thereby decreasing the accuracy of any measurements sought to be made.
U.S. Pat. No. 4,848,360 to Palsgard, et al., discloses a less intrusive system used to prevent snoring. According to the Palsgard, et al. patent, a microphone placed beneath the patient's mattress may be used to pass sound information to a series of high- and band-pass filters. The filtered signals subsequently are sent to circuitry designed to measure their periodicity and determine whether the periods correspond to typical time intervals for snore-associated sounds. Once snoring is detected logical signals are transmitted to a counter which activates a vibrational device or other anti-snoring apparatus following receipt of a preselected number of signals.
Like the devices disclosed in the Tucker and Virgulto, et al. patents, the system of Palsgard, et al. is not designed as an evaluation tool for the counting of coughs. The Palsgard, et al. system also lacks storage means beyond the digital counter used to determine if continuous snoring is occurring, preventing any off-line evaluation or visual confirmation of the sleeper's activities. Because some snoring may not alter respiration sufficiently to result in determinable movement by the patient, the system disclosed in Palsgard, et al. similarly lacks any motion detecting means.